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Friday, April 13, 2018

Northern Snakehead Expanding Range, by Don Orth

On May 14, 2002, a Maryland angler caught (and released) a 17 inch snakehead fish in a stormwater detention pond in Crofton, Maryland. Six weeks later another angler caught a 26 inch snakehead. Juveniles were dipnetted a week later, confirming a reproducing population. The snakehead population was eradicated but Northern Snakehead Channa argus were already in the Potomac River and tributaries (Odenkirk and Owens 20007). Yet, this fish is native to China and North Korea and in 2005 Congress directed the U.S. Fish and Wildlife Service "to identify, contain, and eradicate the species.” The family of snakehead fishes (Channidae) includes 26 airbreathing fishes native to Asia, Malaysia, Indonesia, and tropical Africa. Several species have been introduced to the US for sale in ethnic markets and restaurants that hold live fish for customer selection. Ten species of snakehead (Channa spp) were deemed high risk for establishment (Herborg et al. 2007). Uncertainty about this exotic fish resulted in exaggerated fear-based reactions. Snakehead TerrorandSwarm of the Snakehead are full-length horror films based on the exotic snakehead. Should you be terrorized?

What
do we know about Northern Snakehead? Northern Snakehead are readily
identified by the long dorsal and anal fins, pelvic fins located beneath
the pectoral fins, a truncate caudal fin, and a large mouth that
extends far beyond the eye. The mouth attracts most attention with its
large canine-like teeth on upper and lower jaws. The coloration is
golden tan to pale brown or olive with a series of dark irregular
patches on sides and saddle-like blotches across the back. The largest
specimens from Virginia waters were 34 inches (Odenkirk et al. 2013),
but larger ones are reported by bowfishers and anglers. The Maryland state record is 18.42 pounds. Northern
Snakehead are effective ambush predators as adults and dietis mostly
banded killifish Fundulus diaphanous, white perch Morone americana,
bluegill Lepomis macrochirus, and pumpkinseed sunfish Lepomis gibbosus, all common fishes(Odenkirk and Owens 2007). Northern Snakeheads are commonly caught by bass anglers
and bowfishers target them.

Northern Snakehead Channa argus Photo by D.J. Orth.

How far might they spread? Since the nonindigenous Northern Snakehead became
established in the Potomac drainage, the fear factor has diminished and
investigators have discovered some critical information about this fish in its
new habitat. The potential for
widespread dispersal through North America is very great considering its broad environmental
requirements and adaptations (Herborg et al. 2007), as well as the
multiple reservoirs in the Northern Virginia region. Northern Snakehead has spread through the
Potomac (Fuller et al. 2015) and now extends throughout the lower Potomac from
Great Falls to the mouth, including some tidal portions with moderate salinity
(up to 7.6 ppt; Starnes et al. 2011).
Also, it has recently spread to the Rappahannock drainage (Strong 2013). These conditions make the Potomac region relevant
to continent-wide spread as well as a model system for evaluating
naturalization and understanding migration and movement patterns in the
Northern Snakehead.

Distribution of knownNorthern Snakehead Channa argus populations in the United States (Fuller et al. 2015.

Suitability of the environment for the Northern Snakehead (Herborg et al. 2007).

Are they expanding their range? Yes, Northern Snakehead is more widespread than other invasive fishes including the Blue Catfish Ictalurus furcatus and Flathead Catfish Pylodictus olivaris (Love and Newhard 2018). They are now found in "nearly every major drainage of Maryland's tidal portion of the Chesapeake Bay watershed" (Love and Newhard 2018). Snakehead have colonized new watersheds via migrations through waters with salinities exceeding 6-12 ppt. Movements increased in response to water temperatures warming above 14°C
(Lapointe et al. 2013). Gascho Landis et
al. (2011) characterize the pre-spawn season (April-June) as a time of high
feeding and gonad growth. Spawning
begins when water temperatures reach 26°C and may spawn multiple times occur
over a long period; nest guarding
occurs from July to mid-September. The population likely expands periodically during times when freshwater inflows permits the Northern Snakehead to move with freshwaters. Northern Snakehead is also established in the Mississippi River basin in Arkansas.

Genetic analysis supports the hypothesis that five genetically distinct populations of Northern Snakehead occur in the US (Resh et al. 2018. The Arkansas population is most genetically differentiated from the Potomac River population and effectively population sizes are high.

Snakeheads are a favored food fish in India and parts of Asia. Here and elsewhere they are specialty foods available live for selection at upscale restaurants. Management of the Northern Snakehead and other snakehead species is complicated by trade in the live food fish market. China has been the largest exporter of snakehead (Snakehead Plan Development Committee 2014). As if the US-China trade policy needed any more sources of conflict, the snakehead is likely far down the list of trade issues. Many states and provinces have enacted bans on possession, transport, and breeding of snakehead fish. Since snakehead are "injurious" wildlife under the Lacey Act, the U.S. Fish and Wildlife Service Office of Law Enforcement seizes illegal shipments. Eradication of Northern Snakehead in open systems, such as the Chesapeake Bay, is unlikely given the large effective population size (Resh et al. 2018). But don't feel terrorized. An effective snakehead solution will rely on dealing with the unauthorized release into public waters. Humans are the vector. Humans are the solution. References

Owens, S.J., J.S. Odenkirk, and R. Greenlee. 2008.
Northern snakehead movement and distribution in the tidal Potomac River system.
Proceedings of the Annual Conference of
the Southeastern Association of Fish and Wildlife Agencies 62:161–167.

Starnes, W.C., J. Odenkirk, and M.J.
Ashton. 2011. Update and analysis of fish occurrences in the lower Potomac
River drainage in the vicinity of Plummers Island, Maryland—Contribution XXXI
to the natural history of Plummers Island, Maryland. Proceedings of the Biological Society of Washington 124(4):280-309.